Quantum computation and quantum information* MARIUS NAGY* and SELIM G. AKL† School of Computing, Queen’s University, Kingston, Ont., Canada K7L 3N6 (Received 13 May 2005; in final form 8 July 2005) The paper is intended to be a survey of all the important aspects and results that have shaped the field of quantum computation and quantum information. The reader is first familiarized with those features and principles of quantum mechanics providing a more efficient and secure information processing. Their applications to the general theory of information, cryptography, algorithms, computational complexity and error-correction are then discussed. Prospects for building a practical quantum computer are also analyzed. Keywords: Quantum mechanics; Qubit; Superposition; Interference; Measurement; Entanglement; Quantum gates; Information theory; Cryptography; Quantum computer; Algorithms; Complexity; Error-correction; Experiments 1. Introduction and overview Quantum computation and quantum information can be defined as the study of information processing tasks accomplished using quantum mechanical systems. One of the most striking aspects of it is the complete uncertainty about its future. It could rise to meet the expectations of enthusiasts of the field, causing computer science to be reconsidered (and effectively rewritten) in the new quantum light. In such a case, quantum computers and practical applications of quantum information theory will substantially impact our everyday life. But it may also happen that quantum mechanics will one day be disproved or the formidable obstacles towards making quantum computers a viable technology will prove insurmountable. This will leave quantum computation and quantum information as abstract mathematical curiosities, without substance. 1.1 Origins of quantum computing Most people involved in the field associate the birth of quantum computation and quantum information with a talk Richard Feynman gave at MIT in 1981 (see [80] for the journal The International Journal of Parallel, Emergent and Distributed Systems ISSN 1744-5760 print/ISSN 1744-5779 online q 2006 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/17445760500355678 *This research was supported by the Natural Sciences and Engineering Research Council of Canada. † Email: akl@cs.queensu.ca *Corresponding author. Email: marius@cs.queensu.ca The International Journal of Parallel, Emergent and Distributed Systems, Vol. 21, No. 1, February 2006, 1–59